This invention relates to a method for winterizing (dewaxing) of vegetable oils, comprising neutralizing the oil, chilling, mixing with an alkaline solution, gentle stirring during a resident time in order that waxes and other high melting matters are precipitated, and removal of same.
Some oils, like sunflower oil contain small quantities of high melting matter, e.g. waxes and tristearines, which precipitate during storage in refrigerators and also after prolonged storage at ambient temperature. In the vegetable oil industry different methods have been applied since a long time in order to remove such high melting matters from the oils in question, especially sunflower oil.
Thus one method has been applied, in which the refined oil is chilled to a temperature, at which said matters crystallize after some time and can be removed by filtration. Due to the crystal structure and the high viscosity of the oil at the filtering temperature this is a difficult and tedious procedure, which is also expensive. Thus more efficient methods has been sought for removal of waxes and other high melting matters from vegetable oils. One method of the art mentioned introductorily is disclosed in U.S. Pat. No. 4,035,402.
This process for dewaxing of vegetable oils comprises the steps of
(a) prerefining of vegetable oil till it contains less than 1000 ppm soap and less than 1000 FFA and chilling to a temperature below 15.degree. C.;
(b) holding said oil at said temperature for more than one hour;
(c) mixing of the oil from step (b) with an alkaline water solution;
(d) agitation of the mixture from (c) in a low shearhigh circulation manner for at least 1/2 hour to uniformly disperse the alkaline solution without forming an inseparable emulsion;
(e) separating the agitated mixture to provide a wax containing water phase and an oil phase.
It is stated that 10 to about 30% (weight) alkaline solution, calculated on the mixture so obtained, shall be added. This means that 11-43 kgs alkaline solution are added to 100 kgs oil. It is stated as quite important that if for instance NaOH is used as alkali, the concentration of same shall be within an interval of 1.0-2.5% (weight) in the alkaline solution, as the process is said not to be satisfactorily operable at lower or higher concentrations.
In fact it has become obvious that it is difficult to get a process of this type to operate well. Thus there is a need for a process of the art mentioned introductorily, which operates well, in which there are only minor losses of neutral oil and which is economical in operation.